Contigs are contiguous fragments of DNA sequence from an incomplete draft genome.
Chimeric contigs are contigs that combine sequences from more than one genome. Short sequence reads from two different genomes can be incorrectly assembled into one contig due to a short region of similar sequence. Chimeric sequences are usually more frequent in 16S amplicon sequencing than in full genome shotgun sequencing.
Chimeric 16S sequences are merged rRNA seqments from different (but usually closely related) bacteria.
How to identify chimeric 16S sequences?